chapter  4
18 Pages

The lens and perspective

The eye/brain judges depth by binocular cues (available to two eyes) and monocular cues (available to one eye). Because the eyes are about 6 cm apart the retinas of the eyes receive slightly different images. It is the comparison of these two images and by movement of the head that information about depth is achieved with binocular vision. The short fashion for three-dimensional films in the 1950s replicated stereoscopic vision by having two overlapping images forming the projected image that were separated when viewed by green and red spectacles. Apart from this fashion, a television or film shot is a ‘one-eyed’ system and indications of depth are achieved by:

* relative size of known objects or same size objects; * linear perspective – parallel lines converge in the distance (e.g.,

looking along railway lines); * overlap – any subject that obscures another subject is perceived as

being closer to the lens; * relative brightness – subjects that are clearer and brighter are per-

ceived as being closer to the lens than subjects at a distance; * motion parallax – as the camera’s viewpoint changes, more distant

objects will move more slowly than objects close to the lens; * texture gradient – regular size objects (e.g., blades of grass, fabric

weave) will diminish in size as they recede from the lens; * height in the frame – a subject that is higher in the frame (and

smaller) than a similar foreground subject is perceived as being further away.